The vernal equinox occurs in March when the sun appears to be crossing the celestial equator. During this time, the sun is usually heading north. The autumnal equinox occurs in September when the sun crosses the equator as it moves towards the South Pole. On these days, the sun is directly over the equator. This results in equal durations of day and night.
The solstices occur when the earth is at its farthest distance from the sun. It occurs due to the elliptical shape of the earth’s orbit around the sun. This means that there are two solstices and ruing this time the sun appear to be farthest, either north or south, from the celestial equator. Summer solstice occurs when the sun is at the maximum point in the sky at midday (Karttunen, 341). The winter solstice, on the other hand, is when the sun appears to be at it at its lowest point at midday. During the summer solstice, the earth is closer to the sun than during the winter solstice. This means that hotter temperatures are experienced in the summer solstice and cooler ones in the winter solstice.
A total eclipse of the sun occurs when the moon entirely covers the sun from being seen from the earth. This leads to complete darkness for the duration that the moon covers the sun. Total eclipse take places when the moon is between the sun and the earth. Therefore, some parts of the earth do not receive light even during the day. During a total eclipse of the sun, the moon appears larger than the sun hence covering it entirely. An annular eclipse of the sun, on the other hand, occurs when the moon partially covers the sun from being seen. It appears smaller than the sun, and a solar disk or annulus of the sun is visible. The two types of solar eclipses occur because of the fact that when a solar eclipse takes place, the shadow cast on earth may be totally dark (umbra) or partially dark (penumbra). The umbra results in a total eclipse of the sun whereas the penumbra results in annular eclipse of the sun (John, 115).
Copernicus developed the heliocentric model for explaining the cosmic and heavenly bodies. This model was centered on the sun. This also meant that there were no forces associated with the motion of any planets or other heavenly bodies. Furthermore, he believed that all objects revolved around the sun in a westward direction. The retrograde motion of planets means that movement is slowed down before stopping, reversing its direction and moving in a westward direction for a short direction. This is unconventional since most heavenly bodies appear t move from east to west when observed in the earth’s sky at night (Kutner, 243).
Retrograde motion occurs for any planet that is located further away from the sun than the earth. The change in the direction of motion of the outer planet relative to stars is because the earth revolves at a faster speeder hence overtaking the outer planet. After overtaking the planet, it appears to change its direction of motion relative to the stars. After the earth has well overtaken this planet, it appears to resume it normal direction relative to the stars.
Uranus was among the first planets discovered by astronomers since it was easily visible in the sky. Newton’s Laws of gravitational attraction were used to predict the position and orbit of this planet around the sun. Newton’s Law of gravitational attraction was based on the fact that the gravitational force of attraction between two bodies depended on the mass of both bodies and the distance of separation between the two. However, physicists and astronomers found that the path taken by Uranus did not coincide with their calculations as per Newton’s laws. This made scientists believe that another heavenly body might exist in the vicinity of Uranus, which affected its path around the sun such that it did not follow Newton’s laws. In 1845, two astronomers, used data on Uranus and Newton’s law to determine the mass of the new planet (Neptune) and its distance from the sun and Uranus. The predictions were correct, and they were confirmed in 1846 by another astronomer (Seeds and Dana, 146).
Reflection is the adjustment in the direction of the rays of light due to the presence of a mirror in the path of a light beam. Reflection involves a precise change in the direction of light since the angle of incidence is the same as the angle of reflection. On the other hand, refraction is the bending of light as it moves from one medium to another. The bending occurs due to the different refractive indexes of the two mediums. Although, the angle of incidence is not equal to the angle of refraction, the refractive indexes of the two media can be used to predict the angle of refraction for various angles of incidence.
Telescopes use the principle of refraction to converge the rays from a distant object using a convex lens. The rays are then focused using a concave lens. Similarly, the incoming light from an object can be focused using multiple mirrors and the principle of reflection. Refraction is used to make small telescopes while reflection is used to make larger telescopes.
Reflecting telescopes do not have difficulty with chromatic aberration. This arises in refraction telescopes due to the production of multiple wavelengths of light by a lens as refraction occurs. This may portray the wrong color of the object being viewed. Furthermore, it is quite costly to construct refractive telescopes due to the high cost of refractors that must be used especially if one wants to construct a very strong telescope. The aperture in reflecting telescopes is not limited to a small size as in refractive telescopes. This means a clear image of a very distant object can be obtained better using reflecting telescopes than using refractive telescopes.
Interstellar gas clouds are structures containing gas in space. These clouds are visible through the use of telescopes since they are invisible to the human eye. The telescopes must capable of spanning the entire all wavelengths of light on the electromagnetic spectrum. The electromagnetic spectrum of hydrogen varies since it can harbor one or two electrons in its outermost energy level. The colors emitted depend on the wavelengths of specific media. This depends on the distance between this cloud and nearby stars. If it is very far from stars, the cloud will reflect a sky blue color. This is because the electrons of hydrogen will not be energized by the energy of the stars since they are too far. However, if the cloud is located near stars, the hydrogen atoms will be ionized hence resulting in a red glow from the cloud.
Doppler shift is a condition whereby dark lines appear in the spectra of a light source, for instance, a star because the relative motion of the star towards or away from a heavenly body. It occurs due to shifting of the wavelength of the light being emitted. For the Doppler shift to be effective the observer and the source must be perpendicular to each other. This is because light travels in a straight line. The spectrum of a star can be used to determine using Doppler shift. However, the Doppler shift cannot be used to show celestial activity across a spherical space since it relies on the fact that there has to exist a perpendicular alignment between the light source and a heavenly body.
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Karttunen, Hannu. Fundamental Astronomy. 5th ed. Berlin [etc.: Springer, 2007. Print.
Kutner, Marc Leslie. Astronomy A Physical Perspective. 2nd ed. Cambridge, U.K.: Cambridge
Seeds, Michael A., and Dana E. Backman. Astronomy: The Solar System And Beyond. 6th ed.
Belmont, CA: Brooks/Cole, Cengage Learning, 2010. Print.